Optimization of Capillary Irrigation System for Field Application

Subsurface micro-irrigation systems are widely considered as a promising means to increase water use efficiency in agriculture. An economical, less laborious, and water-efficient type of capillary irrigation system (CIS) was developed. Optimisation of this CIS for greater efficiency requires adequate knowledge of the accurate surface wetted radius under different capillary node sizes and soil textures. A point source type for the different capillary node sizes 12.7 mm, 19.1 mm, 25.4 mm, and 50.8 mm diameter, installed in rectangular containers were studied under six soil types (Itagunmodi series, Egbeda series, Oba series, Iwo series, all belong ultisol, Apomu series (inceptisol) and Fine sand as control), and compared with hand irrigation (watering can) in a screen house experiment. Soil moisture spread around the capillary nodes was monitored, and the empirical equations for predicting soil surface wetted radius for each capillary node size were developed and verified in the field. The results showed that soil wetted radius increases with an increase in the soil clay content, and the soil type with the highest clay proportion (18%) generated the maximum wetting front. Sorptivity correlated with soil moisture spread, but the consistency of the wetted area depended on the soil clay content. Capillary node size 12.7 mm and 50.8 mm diameters performed better and enhanced soil water distribution across different soil types than other capillary node sizes due to their narrow-node and pore-number effects. The lateral spacing of these node sizes per unit land area for optimal performance can be guided by the models developed in this study.